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TCRP J-6/Task 75 (WOD 51): Guiding the Selection and Application of Wayside Energy Storage Technologies for Rail Transit and Electric Utilities FOREWORD By Lawrence D. Goldstein Staff Officer Transportation Research Board TCRP Web-Only Document 51 (WOD 51) is a comprehensive guide for identifying and implementing effective wayside energy storage systems for rail transit. Energy storage applications addressed include braking energy recapture, power quality voltage sag regulation, peak power reduction, and the development of energy storage substations. The guide identifies opportunities and constraints along with analytical methods for determining potential benefits for cost-effective energy storage applications. It takes the reader through required evaluation steps: needs assessment, simulation modeling, measuring potential economic benefits, and selection of alternative applications. The study concludes that wayside energy storage devices can be designed to help resolve propulsion power demands while addressing issues of voltage sag and energy inefficiency in the context of increasing utility costs. Rail transit has been in the midst of an extended period of increasing ridership as a byproduct of changing economic conditions along with a rise in price of gasoline. This increase in demand is taxing the ability of transit systems to meet capacity requirements in the context of limited system-wide revenues. To compound the problem, the price of electricity that powers rail transit systems is rising because of a rapid growth in demand for electrical power nationally coupled with limited capacity of an already strained electrical grid. In addition, existing rail power substations may not be adequately equipped to accommodate operation of heavier trains with more passengers, to operate higher performance trains, or to operate more frequent trains on shorter headways. This research was predicated on the belief that there is a way out of this dilemma for rail transitâusing trackside energy storage systems. Successful applications of test systems have previously demonstrated that energy storage can be used to recycle regenerated energy from braking, to reduce voltage sag between existing substations, and to reduce peak power demands that help to decrease system-wide electric utility costs. In particular, trackside energy storage units in the form of advanced batteries, electrochemical capacitors, and flywheels have evolved in recent years; and several countries have developed pilot energy storage programs.
Other than in a few scattered trials, however, energy storage is new to U.S. transit agencies. There appear to be a variety of reasons for this lack of experience. The average transit agency is often overwhelmed by the need to assimilate knowledge on new storage technology quickly and to learn how to perform necessary engineering analyses for efficient design and operation of available energy storage technologies while experiencing an ever-increasing demand for limited financial resources. Transit agencies have also experienced a need to understand the current state of energy storage technology, the role of utilities as potential partners, and the expected direction of new research and its affect on transit operations. Of particular interest is the fact that, although saving energy is often a prime motivating factor for energy storage, careful analysis is required to determine the payback period. Using the guidance provided, readers will also find this study helpful when considering potential benefits linked to solving associated problems: peak power reduction to offset utility charges, power quality improvement through elimination of power voltage sag, and use of energy storage as a replacement for more costly energy substations. This study leverages work previously prepared by APTA and supported by TCRP that helped to create the Energy Storage Research Consortium. APTA and the Electric Power Research Institute jointly established the consortium, bringing together a diverse member base: Sandia National Laboratories; several transit agencies including the Washington Area Metropolitan Transportation Authority, Los Angeles County Metropolitan Transportation Authority, New York City Transit, the Long Island Railroad, and Bay Area Rapid Transit; state research organizations including California Energy Commission, Sacramento Municipal Utility District (SMUD), New York State Energy Research and Development Authority, and the New York Power Authority; and consultants from Systra-USA, Inc. The consortium initiated the energy storage analysis program by performing a needs assessment for rail transit agencies. This needs assessment recommended preparation of a technology awareness study to help agencies examine potential use of energy-saving technologies such as wayside energy storage devices. In response, WOD 51 identifies and describes the engineering analyses required for selecting and sizing applicable energy storage technologies. The various study components include an evaluation of the problems that wayside energy storage could solve plus a review and analysis of the detailed computer simulation methods needed to assess performance and calculate potential rate of return. The study also examines how agencies might benefit from collaboration with electric utilities. The primary audience for this study includes transit agencies, energy storage vendors, and utilitiesâall of whom need to join forces to implement a successful wayside energy storage system. In particular, through use of this guide, transit agencies can begin to look at what is involved in implementing energy storage programs. The study will provide particular value as it helps agencies to identify what steps are necessary to determine the appropriate energy storage application, the physical location of the devices, and the potential for cost recovery. Such procedures would serve as input to full system design or procurement.
